Electron beam furnace



Feb. 16, 1965 c. w. HANKS 3,170,019

4 ELECTRON BEAM FURNACE Filed Jan. 15, 1962 3 Sheets-Sheet 2 INVENTOR. w amass ZdJ/mvzs FIG-4 BY Feb. 16, 1965 c. w. HANKS 3,170,019

ELECTRON BEAM FURNACE Filed Jan. 15, 1962 3 Sheets-Sheet 3 FIG-5 v INVENTOR. tuna .55 1d. Ham .5

ATJ'OPNEK! United States Patent 3,170,019 ELECTRON BEAM FURNACE Charles W. Hanks, Orinda, Calif., assignor t Stauffer Chemical Company, New York, N.Y., a corporation of Delaware Filed Jan. 15, 1962, Ser. No. 166,341 3 Claims. (Cl. 13-31) This invention relates to an electron beam furnace which employs a magnetic field for guidance of electrons and, more particularly, to a furnace which heats by bombardment with at least two electron beams, and all beams are guided by a single unidirectional magnetic field which influences the path of each electron beam projected transverse thereto in a different, but predictable manner dependent upon the direction of electron velocity in the particular beam. This application is a continuation-in part of my co-pending application, Serial No. 37,615, filed June 21, 1960, now abandoned, for Electron Beam Furnace With Low Beam Source.

One type of electron beam furnace includes an envelope which is continuously evacuated to the order of one micron of mercury and into which a metal is delivered and there fed progressively into a target zone or melting station where it is bombarded by a high-energy electron beam which progressively melts the material. A crucible or mold, preferably water cooled, is also provided within the furnace enclosure and situated so as to receive molten metal dripping from the raw material which is under bombardment by the electron beam. Additionally, the surface of the molten material in the open portion of the mold is bombarded by high-energy electrons in order to keep a pool of molten material at the top of the crucible for controlled gradual solidification into an ingot which is withdrawn from the bottom of the mold. By maintaining a pool at the top of the ingot, rather than permitting solidification of each drop as it falls onto the ingot, the ingot is formed more uniformly.

When materials, including metals, are melted in an electron beam furnace, there is unavoidably generated at the high temperatures involved, a certain amount of gas vapor which is desirably removed as rapidly as the capacity of the furnace chamber evacuation system permits. However, the presence of substantial gas and vapor often subject electron guns which are located in the vicinity of the melting operation to damage. A particularly troublesome condition arises when the gas ions move into the field of the gun and Set up a short circuiting flow of electrons between the cathode and anode of the electron gun. Additionally, heavy ions frequently formed during vaporization might themselves cause electron gun dam age if attracted at high velocity to the field of the gun. Moreover, if the guns are too close to the melt zone, they are subjected to damage resulting from splatter of the melt and from condensation of vapor. Consequently, it is preferred to space electron guns from the mold and employ some means, preferably a magnetic field, for focusing the electron beams. However, where, as here, more than one gun is employed, difiiculty has been encountered when electrons strayed from their influencing magnetic field into an adjacent magnetic field. If the adjacent field is in a different direction, such straying electrons might be diverted from their intended trajectory and thereby rendered ineffective. Moreover, such ice diverted electrons may even do harm by bombarding a furnace component, such as one of the electron guns.

It is, therefore, an object of this invention to provide magnetic fields for guiding electron beams, which fields do not adversely affect the trajectory of other beams.

It is a further object of this invention to provide an electron furnace having at least two electron guns which project their beams in diametrically opposite directions, both beams being influenced by the same magnetic field in a different manner and all electrons in each beam being influenced by the magnetic field in the same manner.

It is a further object of this invention to provide a unidirectional magnetic field which infiuences in a different, but predictable manner, electron beams projected across said field from diametrically opposite directions.

This invention contemplates the provision of at least two electron guns, each adapted to project an electron beam to bombard and heat a separate target. This is accomplished by projecting the beams in diametrically opposite directions across a unidirectional magnetic field so that the electrons are diverted in different directions, under forces transverse to their separate directions of velocity, each to bombard its specific target. In the preferred embodiment of the furnace, material is supported above the open top of the crucible or mold and it is desired to bombard both the raw material to melt it initially and the molten material at the top of the mold for maximum uniformity of solidification. In this arrangement, a unidirectional magnetic field is established across the mold and the electron guns are arranged on diametrically oppoite sides of the mold and aimed to project their beams across the mold in directions transverse to that of the magnetic field. Since the electron beams are influenced by a force acting at right angles to both the magnetic field and the direction of electron velocity, beams which are projected in opposite directions will be deflected in different directions. In the preferred embodiment here, one beam will be deflected upward to impinge against the raw material and the other will be deflected downward into the open top of the mold.

Other objects and advantages of this invention will become apparent to those skilled in the art when the description following is read in view of the accompanying drawings wherein:

FIG. 1 is a side elevational view in section of an electron beam furnace embodying the present invention;

FIG. 2 is a plan section view taken along line 2-2 of FIG. 1;

FIGS. 3 and 4 are schematic representation of the influence of magnetic field on electron beams for material being fed to the melting zone vertically and laterally, respectively;

FIG. 5 is a side elevation in section of another form of furnace embodying this invention; and

FIG. 6 is a plan section view taken along line 6-6 of FIG. 5.

Referring now more particularly to the drawings, the electron beam furnace of this invention includes an enclosure or envelope 10 which is continuously evacuated to a high vacuum in the order of one micron of mercury, by operation of a source of vacuum shown generally at 12 which is in open communication with the furnace enclosure. A crucible or mold 14, which may be formed with a jacket 14a for circulation of cooling water, is

situated within the furnace enclosure in order to receive the molten material dripping from the raw material 15 after bombardment by an electron beam. Preferably, the mold 14 is also open at the bottom so that as the molten metal 16a dripping therein is cooled and becomes solidified it many be withdrawn from the bottom as a solid ingot 16 by any suitable means here shown schematically as feed rollers 17. The raw material may be delivered to the furnace in any form and by suitable means be presented progressively to a melting station or zone above the open top of the mold 14 wherein it is bombarded by an electron beam. For example, the raw material may be in the form of bar stock 15 which may be fed directly by any suitable means 19 until the end thereof 15a is positioned at the target zone of an electron beam 21 being projected from an electron gun 22. Under the bombardment of the electron beam 21 the temperature of the end 15a of the bar stock is raised appreciably until it melts progressively and drips into the molten pool 16a on top of the ingot 16 being formed within the mold 14. This molten pool is itself maintained at high temperatures by bombardment from an electron beam 23 being projected from second electron gun 24.

The particular guns employed in the furnace of this invention may be of suitable structure to generate and accelerate a directional beam of electrons at a high velocity to a target remote therefrom. Such an electron gun may include an electron-emissive filament or cathode 28, a focusing electrode 27, and an anode 29 for projecting the emitted electrons into a high velocity beam. The electron gun may be energized from a conventional power supply 30 delivering in the order of to kilovolts.

The electron guns 22 and 24 are disposed at diametrically opposite positions spaced laterally from the mold 14 and they are aimed to project their electron beams in opposite directions across the top of the mold as they are influenced by the magnetic field. The guns 22 and 24 need not be aimed horizontally but they must be aimed parallel to the diametrical plane D extending between them (FIG. 2) so as to be projected from diametrically opposite directions into the space between the two targets, i.e. the melting zone 15a at the end of the raw material and the molten pool 16a in the top of the mold.

In conjunction with the diametrically opposed electron guns 22 and 24 the invention contemplates the provision of a unidirectional magnetic field which is transverse to the direction of the electron beam. In the embodiment illustrated in FIGS. 1 to 3, one pair of pole faces 41 and 42 on magnet 43 is disposed along one side of the crucible 14, and a second pair of pole faces 44 and 45 on magnet 46 is disposed on the opposite side of the crucible. The magnets 43 and 46 are energized by windings 47 and 48 which are energized from a power supply 49. One pair of like poles 41 and 44 is disposed on one side of the plane D of the crucible 14 which extends toward and in the direction of the electron guns 22 and 24 and the other pair of like poles 42 and 45 are on the other side, so that the magnetic fields between the pole faces of both magnets 43 and 46 are in the same directions, thus creating a unidirectional magnetic field across the crucible 14 as shown in FIG. 2.

In FIGS. 1 and 3, with pole pieces 42 and 45 both represented as south poles, the magnetic field is in the direction entering the plane of the drawing, as represented by small crosses in the conventional manner. Since the charged particles are subjected to a deflecting force transverse to both the field and the direction of particle velocity, electrons traversing the field in different directions will, of course, be deflected in different directions. As shown, the guns 22 and 24 project their electrons in diametrically opposite directions through the unidirectional magnetic fields the beam 21 is projected toward the left in FIGS. 1 and 3 and the deflecting force of the magnetic field curves it upwardly. The beam 23 is directed generally toward the right and the magnetic field deflects it downwardly. Thus, by controlling the magnitude of the magnetic fields and the velocity of the electrons, the beam 21 may be aimed to impinge upon the end 1511 of the bar stock 15 in the melting zone, and the beam 23 is aimed and guided down onto the molten pool 16a in the crucible 14. It is to be noted particularly that if electrons of either beam 21 or 23 pass through the field of the magnet pole faces arranged to influence the opposite beam, they will be diverted by forces in the same direction since the fields are undirectional.

The arrangement of FIGS. 1 to 3 has been discussed with particular application to bar stock being fed vertically downward toward the target area, but it is not intended that the invention should be so limited. For purposes of illustration, FIG. 4 demonstrates that a similar arrangement would be applicable to material, whether it be bar stock 58 or particles fed laterally toward the target area by any suitable means shown generally as a conveyor 59. In this instance, the unidirectional magnetic field would influence beam 21' to curve upward and impinge upon the forward end of the material 58 progressively melting away the leading portion thereof 58a.

In the form of invention illustrated in FIGS. 5 and 6, similar furnace structure 60 is provided including an envelope 61, vacuum sources 62 and a mold or crucible 63. Also provided are feed means 64 for presenting raw material 65 to the melt zone and removal means 67 for withdrawing the ingot 68 from the crucible 63. As in the forms of FIGS. 1 to 4, one electron gun 70 is arranged to project a beam 72 against the lower end 65:: of the raw material, and a second electron gun 73 is provided to project a beam 74 against the molten pool 68a on the top of the ingot 68.

In association with the electron guns 70 and 73 there is provided a large U-shaped magnet 76 including winding 78. The forwardly extending arms 80 of the magnet 76 terminate in pole pieces 82 and 84 of large area embracing the crucible 63. As in the first embodiment the unidirectional magnetic field 86 extends across the top of the crucible to influence the electron beam 72 and 74 by diverting them in opposite directions as a consequence of their opposing direction of velocity.

While preferred embodiments of this invention have been described here, it is to be understood that modifications and changes therein and thereto may be made by those skilled in the art to which it pertains without departing from the spirit and scope of this invention which is to be defined by the claims appended hereto.

What is claimed is:

1. An electron beam furnace comprising a crucible having an open top, a. melting station for material overlying said crucible, means generating a unidirectional magnetic field across said crucible, and a pair of electron guns on diametrically opposite sides of said crucible, said electron guns being aimed to project electron beams transversely in opposite directions across said unidrectional field so that said magnetic field deflects the beam from one of said guns upwardly to said melting station and deflects the beam from the other of said guns downwardly into the top of said crucible.

2. An electron beam furnace comprising a crucible having an open top, a melting station for material above said crucible, a pair of electron guns on opposite sides of the crucible, and a separate pair of magnet pole pieces associated with each of said electron guns for generating magnetic fields across the crucible, said magnetic fields having lines of force in the same direction, one of said electron guns being aimed to project a first beam of electrons so that said lines of force deflect the first beam upwardly against material at said melting station, and the other of said electron guns being aimed to project a second beam of electrons so that said lines of force deflect the second beam downwardly into the top of said crucible.

3. An electron beam furnace comprising a pair of electron beam targets spaced from each other in a first direction, means generating a magnetic field with unidirectional lines of force transverse to said first direction, and a pair of electron guns on opposite sides of said magnetic field, the electron guns being aimed to project separate beams of electrons transversely through said field and in opposite directions so one of the beams is deflected to one of the targets and the other beam is deflected to the other target.

References Cited in the file of this patent UNITED STATES PATENTS Frank Apr. 12,

Candidus Oct. 24,

Smith June 19,

FOREIGN PATENTS France Nov. 14, 

